diff --git a/package-lock.json b/package-lock.json
index fb391fe..eb5295b 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -6,7 +6,7 @@
   "packages": {
     "": {
       "name": "nouislider",
-      "version": "15.5.1",
+      "version": "15.6.0",
       "license": "MIT",
       "devDependencies": {
         "@typescript-eslint/eslint-plugin": "^5.10",
diff --git a/src/nouislider.ts b/src/nouislider.ts
index 727b0ef..c7dec07 100644
--- a/src/nouislider.ts
+++ b/src/nouislider.ts
@@ -70,7 +70,7 @@ type SubRange = number | WrappedSubRange;
 interface Range {
     min: SubRange;
     max: SubRange;
-    [key: string]: SubRange;
+    [key: `${number}%`]: SubRange;
 }
 
 //region Pips